Open-hearth-furnace structure and method of operation



1929- R. B. KERNOHAN ET AL 1,741,025

OPEN HEARTH FURNACE STRUCTURE AND METHOD OF OPERATION Filed Oct. 1. 1921 2 Sheets-Sheet 1 19219 R. a. KERNOHAN :1- AL 1,741,025

OPEN HEART FURNACE STRUCTURE AND "ETH OD O1" OPERATIOI Filed Oct. 1. i921 Z ShQB'LS-Shflflt v 2 Patented ec. 24, 31929 ROBERT E. KERNOHAN, JAJHIES S. LOCHHEAD,

AND WILLIBALD TRINKS, 0F PITTS- nnnen, PENNSYLVANIA EEH-HEARTH-FURNACE STRUCTURE AND METHOD OF OPERATION Application filed October 1, 1921. Serial No. 504,60.

Gur invention relates to the construction of and to the method of operation of regenerative furnaces, and centers in the construction of the passageways and ports through which the combustible substances, ordinarily gas and air, gain access to the furnace chamber and in the means and method by which the How of these substances is controlled and by which mixture of them is eficcted. The end primarily in view is the proper control of i the generation of heat, both in location and in'intensity, together with the possibility of efiecting variation. in these matters, if desired, in accordance-with the progress of the refining operation; the ultimate end is the production of refined material of the desired quality in minimum time and at minimum expense of material and with minimum wear and tear. While not necessarily so limited, our invention is applicable to the circumstances under which we have developed it, namely to open-hearth steel furnaces fired with lean gas, such as producer gas, or blastfurnace gas, and in such application we shall in the ensuing specification describe it. It

will be manifest to one reading the ensuing specification that the invention is well adapted to furnaces fired with fuels which, on account of temperature or dirtiness, cannot be put under pressure or be conducted through metal pipes. But to no such matters 1S the invention limited; its wider and general appl icability will be understood by those skilled in the art of regenerative furnace operation.

In an application for United States Letters Patent filed by Robert B. Kernohan and James S. Lo'chhead, two of the present applicants, October 29, 1920, Serial No. 420,377, an open-health furnace is shown and de: scribed, wherein a' stream of mingled gas and air and a second stream of air alone may be directed into the furnace, the pressures being variable, and the degree of opening of certain passageways being variable, to the end that the flame as projected into and maintained within the furnace may be such in character as to serve best in the refining operation, and to the further end that, as operation progresses, the flame may if desired be modified in character and suited to changing blown in jets forwardly through ducts 9 and conditions of the furnace charge. The present invention is an improvement thereon.

The accompanying drawings illustrate an open-hearth furnace in the construction of which and in the operation of which our invention may be practiced. Fig. I is a view of the furnace in horizontal section, on the plane indicated by the broken line 1-1, F H; Fig. 11 is a View in vertical and longitu nal section, on the plane indicated at II-w-JM Fig. I.

The furnace includes the usual hearth 1 upon which the charge is borne and wher essential refining operation takes Producer gas, preheated in the rage: (not shown) fiows through passage thence it rises through vertical passag y 6, and enters from the rear the medially arranged downwardly inclined tunnel port 4; through this port the stream of gas is carried into the furnace chamber. Atmospheric air, preheated in the air regenerator (not shown) flows through passageway 52; thence it rises in divided flow through two vertical passageways 7 and 8, symmetrically arranged one on either side of the mid-line of the furnace, and enters from the rear the downwardly inclined port 5, over-arching port 4; through this port air is carried into the furnace chamber. Ducts 9 and 10 lead from air passageways 7 and 8 and open into port '2. Of these ducts it is to be observed that they are symmetrically arranged, and that the flow through them will be symmetrical with respect to the mid-line of the furnace; they extend obliquely forward, and the streams flowing through them will converge with the stream flowing directly through the tunnel port t; they open into the tunnel ort 4 at an intermediate point in the length t ereof, and the converging streams will mingle before the mouth of the port is reached. Nozzles 19 and 20 are provided, through which compressed 'air from a supply pipe 21 may be 05 10. In supply pipe 21 is a valve 23 for regulating the flow, and conveniently a second valve 22, for cutting 0d the flow entirely.

In the operation of open-hearth furnaces as common y conducted hitherto, the draft through the furnace has been relatively feeble and combustion has been imperfectly controlled. lhis has been particularly true of furnaces fired with producer gas. The air ordinarily has been drawn through the regenerator and into the furnace merely by the stack effect of the regenerators and uptakes, and only such pressure has commonly been exerted upon the gas as is incident to delivery through a supply pipe. In some cases a blowing fan has been placed in the stream of air supply to the furnace, but there is a practical limitation upon the building up of pressure there: when the pressure exceeds a small amount, leakage through the masonry of the furnace structure becomes too great. It is impossible, because of expansions and contractions incident to service, to build a furnace which shall be tight against such leak-- age. And there is another difiiculty to be dealt with. High pressures and high velocities, very desirable in order to produce a sharp fiame,require that the ports be relatively narrow; and narrow ports do not afford at the discharge end of the furnace unhind-- cred exit for the products of combustion. (lit is of course to be understood, as is intimated at the beginning, that we here are considering an open-hearth furnace of the prevalent regenerative type, in which the flow of the flame is periodically reversed, and in which the same ports serve alternately for the inflow of.

gas and of air and for the outflow of the prodnets of combustion.) Because of these difflow of air and of gas and to the generation ficulties chiefly, and in spite of various relief projects, open-hearth operation has as a matter of practice been limited to low rates of of a consequent long and lazy flame. This flame is still burning when it reaches the ports at the outgoing end of the furnace, and combastion continues through the ports and even down into the regenerators a state of things both wasteful and destructive.

Thewproposal to use dampers for reducing the efiective size of the passageways on the intake end of the furnace, and for so increasing velocity of flow, involves complication of structure, and dampers when present absorb a great deal of heat.

la the operation of our improved furnace described above, compressed air is blown through nozzles 19 and 20 into ducts 9 and 10, This compressed air may be preheated or not, as found desirable or convenient. The jets of air issuing from the nozzles have high 'VGlOCltY- -f10i1'l 600 to 1400' feet per sec-= ond,a matter conditioned upon the actual pressure of the supply and upon the shape of the nozzle and the size and shape of the orilice. This high-velocity iet entrains hot air from the uptake passages if and 8, and induces a flow of air through ducts 9 and it) into the stream of gas advancing through port Thus'the entering stream of air is divided;

one portion is directed into port 4, where it mingles with the gas before entering the furnace chamber; the other portion flows unmingled through port 5 into the furnace chamber. I The relative value of these two portions of the stream of entering air is variable and responsive to the degree of opening of regulating valve 23; if that valve be closed completely, all of the air will enter the fur-' of air advancing to port 5. As valve 23 is gradually opened, such back flow of gas first is stopped, and then streams of air are directed forwardly through ducts 9 and 10 into the stream of gas in port 4. These streams of air increase in volume, and the streams flowing to port 5 correspondingly decrease, as valve 23 is opened wider. @rdinarily from one tenth to one fifth by weight of the air flowing in ducts 9 and 10 is that which flows from the nozzles; the rest is drawn in from the streams of air rising through uptake passages 7 and 8. By properly proportioning in size'ports l and 5, passageways '2 and 8, and ducts 9 and 10, it is possible by the means described to divert through ducts 9 and lO into port a any desired fraction of the streams of air rising through uptake passageways 7 and 8. Indeed it is possible so to divert substantially the whole of these streams; ordinarily it is not desirable in operation to go so far as that, but it is preferable to allow some air to enter the furnace through port 5.

WVhen valve 23 is nearly closed the flame is long and lazy-such a flame in fact as is usual in open-hearth operation as commonly conducted hitherto; if the valve 23 is opened,

the flame is short and sharp. Any; desired efi'ected within the furnace chamber, where" alone combustion is desired, and the passageways and regenerators through which. the outtlowing gases pass are not subjected to the destructive action of combustion in progress Within them. Furthermore, regulation by valve 23 makes possible variation in quality of flame such variation he desired) according to the progress of the refining opera tion: at the beginning of a run the flame may be relatively short and sharp, and toward the end relatively long and lazy.

We. have shown the compressed air supply A ipes 21, together with the connections whic terminate in nozzles 19 and 20 to be suspended, as by chains 24:, and it will be understood that by such means the nozzles lit) '19 and 20, positioned as shown at the intake end of the furnace, may at the outtake end he swung aside, away from the deleterious influences of the outflowing productsofcombustion. As aii alternative expedient,- these pipes may be stationary and the nozzles water-jacketed-an expedient so, well known in the general field of furnace structure as to require no illustration.

The showing afforded in the drawings will be understood to be diagrammatic, and particularly in these respects :-The ducts 9 and 10 are shown as rectangular in cross section and uniform in dimensions throughout their extent. Manifestly they may be particularly shaped according to the teaching of pneumatics to afford in highest degree the eifect described; the nozzles 19-and 20, shown diagrammatically as mere tapered terminations of the feed pipes protruding into the ducts, may be elaborated and refined 111 form; they may be madeof the multipleet type; they may in position be so related to the form of the ducts as best to achieve their 'efl'ect;

a ain the openings through the walls of passa gew ays 7 and 8, through which the nozzles 19 and 20 are'shown to .be movable are, in

order that the structure may be clearly understood, shown diagrammatically as greater in dimensions than in actual building they would be.

As shown in the drawings, the furnace- A reversing instrumentalities are arranged for the'inflow of gas and air at the left-hand end and for the outflow of products of combustionat the right-hand end. At the righthand end of the furnace the valve 22 in the supply pipe 21 is closed and the pipe itself is retracted and the nozzles 19 and 20 are withdrawn beyond the walls of vertical passageways 7 and 8. At the left-hand end the pipe 21 is advanced, the'nozzles 19 and 20 are in position in ducts 9 and 1Q, and valve 22 is open. Gas and air are entering through the ports at the left-hand end and are burning in a flame which sweeps from left to right, and the products ofcoinbustion are escaping through the ports and passageways at the right-hand end. Kt proper intervals of time the furnace is reversed and, incidentally to reversal, the pipe 21 and nozzles 19 and 20 which had been retracted are advanced, those which had been advanced are retracted, valve 22 of the now advanced pipe degree of opening of valves 23 may if desired f be diminished as operation upon a given furnace charge pro resses, to the end that at the 7 beginning the ame may be relatively short and sharp and toward the end relatively long and lazy.

As has been intimated, we do not intend ordinarily to resort to special means for building up pressure on air or gas on the intake end of the furnace nor to special means for drawing the products of combustion out from the outgoing end. Nevertheless, the practice of our invention does not forbid the use of such ancilliary apparatus, if for any reason it be found desirable.

The jets of air entering port 4 through ducts 9 and 10 produce combustion in port/i, to the extent that the air andga's m'ix. Mixture, however, is not complete until the gases have just left nace. just beyond the opening from port 4 is so rapid that an extremely high temperature is attained, in spite of the injection of cold or only slightly preheated air through nozzles 19 and 20. Preheating of this injected air may of course be resorted to, andmay be carr ed to any degree, but ordinarily preheating will not be necessary.

advantage of projectin streams of air at relatively high pressure t rough ducts 8 and It) and forwardly into ports is found in an increased flow of gas, and that without an otherwise requisite increase of ressure in the gas uptake passageway 6. jet of air under high pressure projected from the nozzle into the duct has great kinetic energy, and entrains or induces the flow of large weights of air (five toten times as much as issues in the jets) from the air passageways 7 and 8 through ducts 9 and 10 into port 4. Furthermore, by the use of the jets of compressed air, this projecting of streams of air through ports 9 and 10 is attained without sub ecting the furnace structure to augmented pressure in the regenerators or in the air uptake passageways 7 and 8, and without resort to dampers.

We have consistently throughout the specification spoken of the substance projected through nozzles 19 and 20 as compressed air, and ordinarily compressed air will be best: air is requisite to combustion in ordinary practice, and is one component of the combus tible mixture within the furnace chamber,

But manifestly the jet might be constituted of some other fluid-of steam, for example, or of oxygen. or of a substance which. not entering into the act of combustion, still serves mechanically, to divert the substance of one of the two streams through the ducts i and 10 into the other stream. The arrangement of ports and passageways might be reversed, gas rising through passageways 7 and 8 verted and projected into the air advancin rom passageway 6 through port t.

We claim as our invention:

1.. In a regenerative furnace the combine tion of a furnace chamber, a Minuet-shaped mixing chamber and means for projecting longitudinally of that duct a fiow-impelling et of fluid, substantially as described.

gas port arranged on the medial line of the furnace and opening to the furnace chamber, an air port overarching said gas port, uptake passageways from the air regenerator arranged on either side of the gas 'port and opening to the air port, a duct leading from each of said passageways to said gas port, a fluid conduit terminating in a nozzle extending into each of said ducts, and means for controlling the flow of fluid through said conduits.

2. The method herein described of developing a flame in the chamber of a heating furnace which consists in opening through bifurcated passageways into the furnace chamber an air-supplied conduit, projecting within one of such bifurcated passageways a flowimpelling jet of fluid, and causing the air flowing in the steam so impelled, before influx into the furnace chamber, to mingle with a supply of fluid fuel.

3. The method herein described of developing a flame in the chamber of a heating furnace which consists in opening through bifurcated passageways into a furnace chamber an air-supplied conduit, projecting within one of such bifurcated passageways a flow-impelling jet of fluid variable in intensity, and causing the air flowing in the stream so impelled, before influx into the furnace chamber, to mingle with a supply of fluid fuel.

4. The method herein described of developing a flame in the chamber of a heating furnace which consists in causing the components of a combustible mixture to flow each in its own conduit to the furnace chamber, maintaining a line of communication between such conduits. and inducing flow from one conduit to the other by projecting in such line of com munication a jet of fluid.

5. The method herein described of operating a regenerative furnace which consists in opening a conduit from gas regenerator to furnace chamber, opening a passageway for air from air regenerator into the gas conduit at an intermediate point between gas regenerator and furnace chamber, and projecting within such passageway a flow-impelling jet of fluid.

6. In a regenerative furnace the combination with the furnace chamber of air and gas passageways leading from the regenerators and opening through air and gas ports into said chamber, an interconnecting duct between said passageways and means'for projecting a flow-impelling jet of fluid longitudinally of said duct, substantially as described.

7. In a heating furnace the combination our hands.

In testimonywhereof we have hereunto set with a furnace chamber of means for conveying preheated air at low velocity through an air port to said furnace chamber, means for supplying fuel toa mixing chamber opening through a gas port to said furnace chamber, a duct leading from the air conveyor to the 

